Known types of positive fluid displacing devices which can be used as either a pump or a motor for liquids or gases comprise an eccentrically mounted rotating cam ring and rotor interconnected by vanes defining a plurality of pumping chambers. For purposes of identification, this type of device will be referred to herein as a constrained vane device. The rotor is driven within the rotating cam ring about an axis eccentric to the axis of the cam ring so that the volume of space enclosed by the rotor periphery, cam ring, closure plates, and any two adjacent vanes varies from a maximum to a minimum during each revolution. Such devices traditionally have fixed or variable displacements, depending on the application. Displacement variation is obtained by changing the amount of offset between the axes of rotation of the rotor and cam ring. To accommodate the ever changing relationship between rotor and cam ring, the vanes are pivotally connected at one end to one of the rotating members and slidably received at the other end by the other member. Often, the slidable connection in one of the members is also pivotable. Examples of this general type of fluid displacing devices are disclosed in U.S. Pat. Nos. 1,210,042, 1,941,651, 2,714,372 and 3,426,693.
A primary design problem in these fluid displacing devices is coupling the cam ring and rotor together so that they maintain the same angular velocity over a total revolution and there is zero phase shift between them. Any cyclic difference in the angular velocity of the two rotating members will produce undesirable loads and wear on the coupler and other parts of the device, excessive vibration and fluid pressure pulsations in the system. Angular phase shift between the rotating members can also alter the intended timing of the moving parts so that the maximum capability of the device is not achieved.
One technique for rotating the cam ring and rotor together is to provide one member with pins which move in enlarged holes in the other. A second technique is to mesh the gears of the drive means for each rotating member. The first technique is used in U.S. Pat. Nos. 1,210,042, 1,941,651, 2,714,372 and 3,426,693. The aforesaid U.S. Pat. No. 1,941,651 to Behlmer also illustrates the second technique in FIGS. 6 and 7. Neither technique provides an acceptable solution to the coupling problem of a variable displacement device and they provide only a marginally acceptable solution for a fixed displacement device.